The present invention generally relates to methods of making patterned coatings. The present invention more particularly relates to methods of making patterned coatings by providing a pattern of energy to or removing a pattern of energy from a liquid coating and solidifying the resulting patterned coating.
Many industrial and consumer products contain thin layers of material that are created by disposing a liquid film onto another material and then solidifying the liquid film. Examples include adhesive tapes, abrasive sheets, painted surfaces, magnetic media, component films in LCD displays, etc. It is often desirable to have topographical features or patterns in such layers to impart aesthetic or performance characteristics. Topographical patterns have been created in such layers using a limited number of technologies. These technologies can be divided into two classes, those that create patterns with or in solid material, for example by etching, and those that create patterns with or in liquid material that is subsequently solidified.
The present application concerns pattern formation in liquid materials and solidification of the patterned materials to form topographically patterned coatings. Relevant patterning technologies include: pattern coating and printing methods; replication methods including various molding, embossing, and lithographic processes; and self-organizing phenomena.
Pattern coating and printing technologies are used to selectively deposit liquid material on regions of a surface. Pattern coating methods include: gravure coating, which uses a roll with a pattern of cells to transfer and dispose the coating liquid; patterned die coating, which uses a die with patterned orifices to dispose liquid to certain areas of a surface; spray coating and the common paint brush, which deposit liquid on selected areas of a surface under the spray nozzle or brush. Patterned printing methods include: screen printing, which disposes liquid to a surface through a patterned screen; flexographic printing, which uses a patterned elastomeric surface or printing plate to transfer liquid to a surface; offset printing, where a liquid is transferred from a patterned surface to a smooth intermediate surface and then transferred again to the surface to be coated; and ink jet printing, where drops, mists, or jets of liquid are disposed to a surface. These methods have the common feature of disposing material to a surface in a non-uniform manner. The resultant non-uniform liquid coating may then be solidified to form a topographically patterned coating.
Replication methods can be divided into those where a liquid is disposed to a patterned master, solidified, and then removed from the master, and those where an initially smooth liquid surface is impressed with a patterned tool, solidified, and removed from the tool. The former are variations on molding. The latter are variations on embossing. A common feature of all these replication technologies is that the liquid comes into contact with a patterning tool.
Recently, several new lithographic technologies have been described. Electro-hydrodynamic lithography and thermo-mechanical lithography involve placing a charged or heated mask in close proximity to a liquid photoresist layer. Electro-hydrodynamic or thermo-capillary effects cause the liquid surface to deform and eventually contact protrusions on the mask surface, forming a positive image of the mask structure. The liquid is then solidified in place to form a pattern of areas for subsequent processing. These replication technologies are some of the few that do not rely on solid contact to deform the liquid surface, though in both processes solid surfaces ultimately come into contact with the liquid.
Finally, self-organizing behavior can create topographical patterns. Benard and Marangoni instabilities are common topographical pattern forming phenomena. Benard instabilities develop from gradients in density in a liquid layer. Marangoni instabilities develop from gradients in surface tension due to concentration or temperature gradients in a liquid layer. Both Benard and Marangoni instabilities give rise to patterns, typically cellular or roll-like, whose size and shape can be controlled only within their naturally occurring limits. Under certain conditions, these structures may be solidified into place, leaving topographical patterns corresponding to the liquid flow patterns. In many coatings, these patterns are considered defects. A major limitation of purposeful application of self-organized patterns is that the patterns are significantly constrained by the structure of the fluid instability.